Some Weeds Were Not Always Weeds

Pampas grass was planted intentionally a long time ago, but then became a weed.

Weeds can be so very sneaky; getting into the weirdest places, and taking on all sorts of forms. They are mostly annuals or perennials that infest lawns and beds, but can be shrubs, vines and even big trees that grow among desirable plants, in untended areas, in cracks in pavement and even in roof gutters and on flat roofs. Many look appealing at first, but then later get out of control and displace the plants around them, or wreck whatever fence, pavement or building they encounter. Heck, I even suspect that it was a weed that stole my neighbor’s Pontiac!

While the soil is still damp from earlier rain, the most common annual weeds that are just developing are easiest to pull. They will put up more of a fight later, after they have dispersed roots, and the soil has gotten a bit more firm. Perennial weeds that were already established before winter will be considerably more stubborn, but not as stubborn as they will be as the soil dries later. Bermuda grass and crabgrass are always nasty.

The biggest, sneakiest and most stubborn weeds are ironically descendents of substantial perennials, shrubs and trees that were once actually planted in gardens. They are sneaky because they look as pretty as their parents when they first appear, in order to dissuade us from pulling them. The problems are that they are often too abundant, and very often get into spots where they will be problematic as they grow.

For example, Acacia dealbata and black locust are rather appealing trees while they are young, especially when they bloom. This is why they were originally planted in local gardens. It is tempting to allow self sown seedlings to grow instead of pulling them when they first appear. However, because they were not actually planted strategically where they can necessarily be accommodated, they grow in random situations, too near to pavement, fences or eaves, or in areas that are already landscaped. As they mature, they can damage these features or the plants around them.

Privet, pampas grass, castor bean and a variety of palms, acacias, ivies and several other plants that do a bit too well in local gardens have certain potential to become invasive or aggressive big weeds. Tree of Heaven, giant reed, the various brooms and the most invasive of acacias  have not been available in nurseries for many years because they are so problematic, but continue to be some of the most invasive and aggressive weeds in California.


Acacia dealbata

It is an aggressively invasive exotic weed, but at least it is pretty about it.

Some of the worst weeds in California are substantial naturalized trees. The most famous of these is probably the Tasmanian blue gum (eucalyptus), which gets very big very fast, and crowds out other trees and plants in the process. The silver wattle, which is most commonly known locally by the Latin name Acacia dealbata, is even more voracious and prolific. It may seem simple enough to cut down an invading Acacia dealbata before it gets too big, but the seedlings from the original tree may continue to invade unrefined landscapes or wildlands for years afterward.

Even urban Acacia dealbata that lack space to disperse seed are problematic. After only about thirty years, they begin to deteriorate, but can die a slow unsightly death for another ten years! Deteriorating trees are likely to fall without much warning. They can get  more than sixty feet tall, and typically fall intact, so can do considerable damage.

The only attribute of Acacia dealbatais that it can be so visually appealing. The somewhat gray, bi-pinnately compound foliage is very finely textured, and provides just enough shade without being too shady. (Bi-pinnately compound leaves are divided into smaller leaflets, which are also divided into even smaller leaflets.) Individual leaves are about three to five inches long. The fuzzy staminate (lacking petals) flowers that bloom in winter are so abundant that most of the foliage is obscured. The floral fragrance that is objectionable to some is appealing to others.

Nature Is Not Naturally Accommodating

Many trees naturally exhibit irregular form.

Gardening is quite unnatural. It involves unnatural cultivation of mostly unnaturally exotic (nonnative) species of plants. Irrigation delivers more water than seasonal rain provides. Fertilizers contribute more nutrients than endemic soils provide. Pesticides, if necessary, inhibit proliferation of pathogens. Nature simply could not accommodate such demands.

Not only is gardening unnatural, but it also interferes with established ecosystems. Many aggressively invasive plants were formerly desirable exotic plants that naturalized. Many pathogens arrived with exotic plants. Several naturalized plants have potential to distract native pollinators from native plants that rely on their pollination. It is an ecological mess.

Nonetheless, it works. Gardening within the constraints of nature would be unproductive. Most residents of California inhabit chaparral or desert climates that originally sustained limited vegetation. Such limited vegetation sustained a very limited indigenous populace within relatively vast areas. Modern residential parcels would be completely inadequate.

That is the justification for gardening, whether for sustenance, or merely to beautify home environments. Unnatural breeding continues to improve performance of many useful and appealing plants. Unnatural horticultural techniques generate more desirable vegetation within confinement of urban gardens than would naturally inhabit a few acres in the wild.

Nature remains relevant though. All plants originated within nature somewhere. Besides their basic requirements, exotic plants prefer environmental conditions that are similar to those of their natural origin. Some tropical plants crave more warmth and humidity. Some plants prefer more winter chill. Most popular exotic plants rely on supplemental irrigation.

Physical characteristics of many plants necessitate special accommodations also. Roots of plants that naturally compete in dense jungles are likely to damage pavement. Without adequate pruning, native plants that naturally exploit burn cycles can become perilously combustible. Many vines naturally try to overwhelm nearby vegetation and infrastructure.

Not all weeds are unwelcome.

Unplanned acacias certainly put on a show when they bloom. It is not easy to dislike something so impressively colorful.

Even the best tended gardens get weeds. Most weeds, particularly annual and perennial weeds, meet a quick demise by getting pulled out or sprayed with herbicide. A few shrub and tree weeds though, are sometimes allowed to mature into functional members of the landscape.

Many sneak into the garden by growing within overgrown or otherwise concealing shrubbery, where they can hide long enough to get established. Others are left to grow because they are recognized as desirable plants. The main problems is that many end up in situations where they eventually become problematic.

Mexican fan palms are distinctive trees. Unfortunately, many grow below utility cables, because that is where birds drop the seed as they eat the fruit. Unlike other trees, palms can not be pruned around utility cables, so must be removed when they get too tall.

Silk tree, black locust, tree of Heaven and various oaks, pines, acacias and eucalypti are some of the more common trees that can sneak into gardens. Sometimes, they happen to land in good situations. More often though, they get too close to foundations, eaves, pavement or other features that they damage as they grow. Like Mexican fan palms, they are easier to remove while young, before they become problematic.

Pittosporums, cotoneasters and privets are commonly seeded shrubbery with less potential for problems. The main problem with glossy privet is that it can be too prolific and aggressive, so that it can crowd out more desirable plants. Most pittosporums and cotoneasters that get seeded are from plants that are ‘straight species’ (not cloned cultivars or varieties). Those that happen to be from cultivar or variety plants will not be ‘true to type’, which means that they will be more like the straight species than like their parents.

The few fruit trees that can sometimes grow from seed have the same problem, since only some of the more genetically basic types may resemble their parents. Fancier types and (non-sterile) hybrids probably will not. Fruit trees that grow from root suckers of grafted trees instead of from seed will be nothing like the parents, and may produce useless fruit.

Pampas grass is a prolific and sometimes welcome perennial weed near untended parcels or forested areas where pampas grass has naturalized. Broom is a shrubby weed that is even more prolific, but never welcome.

Algerian and English ivy rarely grow from seed, but can be really nasty weeds if they get where they are not wanted. Bear’s breech (or breaches), Jupiter’s beard, calla, mint and various yuccas that were planted may be very difficult to eradicate if they are no longer desirable, or if they migrate into areas where they become problematic.

Weeds Are Full Of Surprises

Pokeweed is rapidly becoming more common.

While it was busy naturalizing in Australia, South Africa and southern South America, the California poppy was getting forced out of parts of its own native range by more aggressive exotic plants that were also busy getting naturalized. Technically, any plant that is not native is exotic. Any exotic plant that becomes naturalized in a foreign environment is able to proliferate without any help, as if it were native. Naturalized exotic plants that get too aggressive become invasive weeds.

Weeds are plants where they are not wanted. This is a very broad definition that includes plants ranging from simple little dandelions in urban lawns to humongous bluegum eucalyptus in forests. Naturalized exotic weeds can be much more problematic than weeds that can only proliferate where they get watered in gardens and landscapes, because they can get established where they are not expected.

Water hyacinth that clogs the Sacramento and San Joaquin River Delta is not often a problem in terrestrial landscapes. However, giant reed, pampas grass, Acacia dealbata and blackberry brambles can infest home gardens just as easily as they infest wild lands. Because they do not need to be watered, they can get established and grow quite large in unused parts of the garden before anyone notices.

Many naturalized weeds somehow seem to much more aggressive and problematic than even the most prolific of native plants. Even the common native lupines are relatively docile compared to annual oat grass. Native blackberry may seem impossible to eradicate, but is actually neither as persistent nor as unpleasant to handle as the exotic Siberian blackberry!

Young weeds are easiest to pull now while the soil is still evenly damp, and young roots are only beginning to disperse. They will be more difficult to pull after roots are dispersed and soil hardens. Tree weeds and large perennial weeds that were cut down last year instead of pulled will likely need to be dug. Bermuda grass is a relatively low perennial grass that always seems to be difficult to dig. Mowing or cutting down annual grass weeds with a weed whacker will not eliminate them, but limits the development and dispersion of seed for the next generation. Burclover, sowthistle, bindweed, purslane, spurge and the various oxalis are some of the other common weeds that really get going this time of year.

Silver Wattle

Silver wattle is a magnificent weed.

Almost everyone on the West Coast of California has encountered silver wattle, Acacia dealbata. Some of us know how resilient it is to most methods of eradication. The more fortunate enjoy its magnificently bloom from a distance. It is almost never planted intentionally. It is an aggressively naturalized exotic species. Most grows wild near roadside ditches. Some invades home gardens.

The profuse and bright yellow bloom of silver wattle is spectacular while most deciduous trees remain bare late in winter. Big and billowy trusses of smaller round floral structures obscure most of their slightly grayish foliage. The many individual staminate flowers within this impressive bloom are actually minute. Their hearty floral fragrance is appealing to some, but objectionable to others.

Silver wattle lives fast and dies young. Some trees are so vigorous while young that they are unable to support their own weight. Without appropriate pruning, they simply fall over. Even stable and structurally sound trees deteriorate after about thirty years. Few survive for fifty. They seed prolifically though! Mature trees can get forty feet tall. The finely textured foliage is bipinnately compound.


French broom seems to be indestructible.

Shortly after silver wattle finishes blooming up high, any of four species of broom begin blooming down low. Brooms and silver wattle often naturalize together. All bloom with the same delightfully brilliant yellow. The four brooms are French broom – Cytisus monspessulana, Scotch broom – Cytisus scoparius, Portuguese broom – Cytisus striatus and Spanish broom – Spartium junceum.

Sadly, none are desirable species. All are exotic weeds. They are only a topic for gardening because they are so aggressively invasive. Not only do they overwhelm and displace native species, but they also enhance soil nitrogen to promote the growth of other exotic weeds! They are unpalatable to deer, and are not bothered by insects or disease. Furthermore, brooms are combustible!

It is best to enjoy their cheery bloom from a distance, where they grow wild where they really should not. The various species tend to dominate distinct regions, with some degree of mingling. Big specimens can get eight feet tall, but do not live long as they are replaced by herds of seedlings. French broom is the only evergreen species; but any can defoliate in response to hot dry weather.

Wild Strawberry?

Wild strawberries are worth salvaging.

Under a bank of carpet roses that I am none too keen on, this grubby ground cover competes with more aggressive weeds. To me, it looks like common mock strawberry, Potentilla indica. I never gave it much though. It seemed to me that whoever had installed cheap and common carpet roses on that bank would have employed a comparably cheap and common ground cover.

The ground cover was more prolific in open spots that were too narrow for more of the roses, and from there, seemed to have migrated under the roses as a second layer of ground cover. It would not have been installed underneath intentionally. It did not occur to me that it may have grown from seed like so many other weeds there, or migrated in from the surrounding forest.

The white flowers did catch my attention though. I was not aware of a mock strawberry that bloomed with white flowers. I really was not concerned enough about it to investigate. This part of the landscape will be getting renovated soon anyway. The roses will be relocated to where they can not extend their thorny canes into an adjacent walkway. Agapanthus will replace them.

Now that I am seeing more of these odd strawberries, I am wondering if this low ground cover that I formerly had no regard for is actually the native wild strawberry, Fragaria californica. Not only should mock strawberry bloom with yellow flowers, but it should also produce more spherical berries. Now I will need to identify it before I either dispose of it, or merely relocate it.

I prefer to not salvage exotic species that exhibit potential to naturalize from landscaped areas into surrounding forests. If this ground cover is wild strawberry, it migrated from surrounding forests into a particular casually landscaped area.

Mediterranean Climate Is Something Special

90925thumbThe climate here is pretty cool, at least in winter. Right now, it is pleasantly warm. It does not often get uncomfortably cold or hot, and when it does, it does not stay like that for too long. In between the warmest days of summer, the nights typically cool off nicely. In between the coolest nights of winter, the days typically warm up nicely. Humidity is normally minimal. Rain is adequate in season.

We have here what is known as a ‘Mediterranean’ climate. Obviously, it is similar to many climates of the Mediterranean Basin. Beyond the Mediterranean region, there are not many other places in the World that enjoy such reliably temperate weather. Most of such places are in southern and southwestern Australia, the Western Cape of South Africa, central Chile, and evidently, right here.

This particular region of Mediterranean climate is quite large, and extends into northern Baja California. Native plants know how to live here, and many of those that are adaptable to landscapes and home gardens can survive quite nicely with little or no irrigation. Some exotic (non-native) plants want climates with more warmth in summer, more chill in winter, or more rain through the year.

The best, as well as the worst, exotic plant species for local landscapes are those that are native to other Mediterranean climates.

The worst are those that are so happy in the local climate that they naturalize and become invasive to native ecosystems. Without pathogens or competing species that inhibited their proliferation within their respective native ranges, many naturalized species are detrimentally aggressive in ecosystems that they invade. Pampas grass, broom and Acacia dealbata are familiar examples.

The best exotics are not so threatening. Australian fuchsia, kangaroo paw, coprosma, westringia, bottle brush, grevillea, dracaena palm and eucalyptus originated from Australia. Lemon verbena, mayten and some salvias are from Chile. African iris, lily-of-the-Nile, bird-of-Paradise and all of the aloes came from South Africa. Olive, oleander, cistus, and all the lavenders are Mediterranean.

Like Peas In A Pod

P90622KGenerally, that is how they are. Almost all perennial pea flowers bloom with the same bright purplish pink color of the bloom in the picture below. That is, of course, before their pods develop, but you get the point. We sort of know what to expect from them.

As I mentioned in the ‘Six on Saturday‘ post last week, from which the picture below originated, variants like the pink bloom in the picture above are sometimes observed. The rare clear white flowers are my favorites. There might be fluffier double flowers too; although, in my opinion, the single flowers are prettier and look more like pea flowers should look.

I also mentioned last week that, although perennial pea has a sneaky way of growing where it is not wanted, it typically does not grow reliably from seed sown intentionally where it might actually be desirable. I have tried. The seed just did not cooperate. I managed to get a few to grow, but only because I put out a few hundred to compensate for the expected minimal rate of germination.

Because I like the white so much, I took seed from a vine that had bloomed with single white flowers. I figured that they would be more likely to produce a few white blooming progeny. I would have been satisfied if only a single vine in a group of several bloomed white, but got only a few vines that all bloomed with the typical bright purplish pink. They were pretty nonetheless, but were ironically removed when the site was redeveloped.

I also collected seed from vines that bloomed with the common single bright purplish pink flowers, just in case the viability rate of their seed might somehow be better. They were sown into a different situation, so even if I happened to know how many of the seed that were sown germinated and grew, it would not be an accurate comparison. Regardless, I was no more impressed with the result. Perennial pea is best appreciated as weed.P90615+++++